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ORIGINAL ARTICLE Table of Contents  
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Role of Orthopedia Homebox Protein in Subclassification of Pulmonary Carcinoid Tumors: Retrospective Analysis of 110 Cases

1 Department of Thoracic Surgery, Omer Halisdemir University Training and Research Hospital, Niğde, Turkey
2 Department of Thoracic Surgery, Ataturk Chest Disease and Thoracic Surgery Training and Research Hospital, Ankara, Turkey
3 Department of Pathology, Ataturk Chest Disease and Thoracic Surgery, Training and Research Hospital, Ankara, Turkey

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Date of Submission02-Mar-2022
Date of Decision24-Apr-2022
Date of Acceptance28-Apr-2022
Date of Web Publication27-Jan-2023


Background: Orthopedia homeobox protein (OTP), highlighted as a sensitive and specific marker for pulmonary carcinoids, may provide a more objective criterion for subclassification. Methods: A total of 110 patients who underwent surgery for pulmonary carcinoids (2009–2019) were included. Gender, age, application complaint, tumor diameter and location, typical and atypical tumor type, lymph node involvement, stage, recurrence, and survival data were evaluated retrospectively with OTP nuclear staining. Results: The sensitivity of OTP was 66.4%. OTP in subclassifying pulmonary carcinoids was not significant. There was no significant relationship between OTP and lymph node involvement, recurrence, and survival. Conclusion: OTP does not provide significant results in the subclassification of typical and atypical carcinoid tumors and the evaluation of recurrence and survival of carcinoid tumor cases.

Keywords: Atypical, classification, orthopedia homebox protein, pulmonary carcinoid, typical

How to cite this URL:
Çetin M, Fındık G, Demirağ F, Türk &, Aydoğdu K. Role of Orthopedia Homebox Protein in Subclassification of Pulmonary Carcinoid Tumors: Retrospective Analysis of 110 Cases. Indian J Pathol Microbiol [Epub ahead of print] [cited 2023 Mar 27]. Available from:

   Introduction Top

Pulmonary carcinoid tumors are classified as typical and atypical carcinoid tumors, and this classification is based on tumor morphology. Although surgery is the main treatment option for both tumor types, the extent of surgery and the multimodal approach differ in typical and atypical carcinoid tumors. Despite the standardization studies to reduce the subjective evaluation of tumor morphology, especially in the mitotic count, existing minimal histopathological differences may cause misdiagnosis and prevent access to optimal treatment.[1],[2],[3],[4]

In recent years, antibody-based studies that can provide a more objective criterion for differentiating carcinoid tumors have increased in the literature. These studies focused on new antibodies, especially the Ki-67 proliferation index, which took place in the 2018 World Health Organization gastroenteropancreatic neuroendocrine tumors (NETs) classification guideline, as well as CD44 and Orthopedia Homebox Protein.[5],[6]

Orthopedia homeobox protein (OTP), a transcription factor with a well-defined role in embryonic neuroendocrine development, has been reported to be a highly sensitive and specific marker for pulmonary carcinoid tumors and has therefore received particular attention in the recent literature.[7],[8],[9] In this study, the aim is to investigate the role of OTP in distinguishing between typical and atypical carcinoid tumors, and also to examine the value of OTP as an indicator of recurrence and survival.

   Methods Top

Local ethics committee approval was obtained for the study (2012-KAEK-15/2079) and the investigation was carried out in accordance with the Declaration of Helsinki.

Between January 2009 and December 2019, 140 patients who were operated on in our clinic with the diagnosis of pulmonary carcinoid tumor were evaluated. Patients who were excluded from follow-up (n = 15) and whose pathology specimen was insufficient for restaining (n = 15) were excluded. The final study population was 110 patients and the study was performed on pathology specimens.

Gender, age, application symptoms, tumor subtype and location, grade, recurrence, and survival data of the patients were evaluated retrospectively. The cases were classified as central or peripheral depending on the presence of endobronchial lesions.

   Immunohistochemical staining protocol Top

All patients were reevaluated by a single pathologist to distinguish between typical and atypical carcinoid tumors. In all cases, we used at least one of the immunohistochemical stains of chromogranin A, synaptophysin, and CD56 to detect neuroendocrine differentiation. Mitotic count was performed manually on areas of 2 mm2 in hematoxylin and eosin (H&E) stained sections as recommended in the 2015 WHO classification, and necrosis was investigated. We considered cases with <2 mitoses per 2 mm2 without necrosis as typical carcinoids and those with 2 to 10 mitoses per 2 mm2 and/or necrosis as atypical carcinoids.[2]

We obtained 4-micron sections from formalin-fixed and paraffin-embedded tissues and applied OTP Polyclonal Antibody (Invitrogen, PA5-31513) to sections prepared at dilution 1:200 on the Dako Omnis system for OTP immunohistochemical analysis.[10] Nuclear staining was evaluated using a semiquantitative scoring system. Cases with no staining were considered "0," and the rest was grouped as "1+" (1-25%), "2+" (25-50%), "3+" (50-75%), and "4+" (75-100%).[7] The OTP groups were also subdivided based on typical and atypical carcinoid distinction.

Statistical analysis

We used SPSS 20.0 (Statistical Package for the Social Sciences, IBM, Chicago, USA) software for statistical analysis. Descriptive statistics were used for the demographic and clinical characteristics of patients. Appropriate tests were applied to test the normality of the data. The student's t-test was used to compare the two groups for normally distributed data. Chi-squared and Fisher's exact tests were used to test independence between categorical variables. Overall survival (OS) was assessed by performing a Kaplan–Meier analysis. The log-rank test was used to compare the factors affecting survival. A P < 0.05 was considered statistically significant.

   Results Top

Among the 110 patients, 51 were male (46.4%) and 59 were female (53.6%). The mean age of the patients was 49.3 ± 13.34 (range: 19–82), and there was a statistically significant difference between typical or atypical carcinoid tumor subtypes for mean age (P = 0.008). The most common presenting complaint was cough, and 25 patients were diagnosed incidentally; 63.6% of the cases were central (n = 70) and 36.4% peripheral (n = 40). After H and E staining, 56.4% of cases were typical carcinoid (n = 62) and 43.6% atypical carcinoid tumors (n = 48) [Table 1] [Figure 1]a, [Figure 1]b. The mean postoperative follow-up was 87 months.
Figure 1: (a) Typical carcinoid tumor with organoid pattern (HEX400). (b) Atypical carcinoid tumor with areas of necrosis (HEX200). (c) "4+" OTP positivity in typical carcinoid tumor (OTPX400). (d) "1+" OTP positivity in atypical carcinoid tumor (OTPX400). (e) Survival Analysis Chart for OTP staining

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Table 1: Age, histological type, presenting complaint, and tumor location

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OTP demonstrated 66.4% sensitivity for pulmonary carcinoid tumors [Figure 1]c, [Figure 1]d. There was no statistically significant differences between the OTP groups in the differentiation of typical and atypical carcinoid tumors (P = 0.249) [Table 2]. Similarly, there was no significant relationship between OTP and lymph node involvement (P = 0.067), recurrence (P = 0.910), and survival (P = 0.240) [Figure 1]e.
Table 2: OTP groups for typical and atypical carcinoid tumors

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   Discussion Top

In the literature, OTP is reported to be a highly sensitive and specific immunohistochemical staining method in distinguishing pulmonary carcinoid tumors from other pulmonary NETs and carcinoid tumors in other organs.[7] OTP expression possesses high sensitivity and specificity (80.2% and 99.4%, respectively), especially in typical carcinoid tumors.[11] With these results, the use of OTP in pulmonary carcinoid tumors is expected to become more prominent and further studies on the subject are suggested.[12]

Studies have pointed out that OTP can be used for the distinction and prognostic assessment of carcinoid tumors, similar to the Ki-67 proliferation index.[13] Swarts et al.[14] indicated that a combination of the Ki-67 proliferation index at 5% threshold value and OTP expression, followed by survival analysis, might lead to the accurate distinction of pulmonary carcinoid tumors. However, Nonaka et al.[7] rejected the significance of OTP in distinguishing typical and atypical carcinoids. In our study, we first evaluated the value of OTP in pulmonary carcinoid tumor classification in the distinction between typical and atypical tumors, and we could not find a statistically significant result.

Several studies have indicated OTP as a strong prognostic factor for survival.[7],[15] Swarts et al.[16] reported remarkably decreased OTP expression in a poor survival group. Papaxoinis et al.[17] evaluated OTP and TTF-1 together and found that TTF-1 "+" and OTP "–" cases showed the worst relapse times, TTF-1 "+" and OTP "+" cases slightly better times, and TTF-1 "–" and OTP "+" cases the best. Another study reported decreased CD44 expression along with decreased OTP expression in biologically aggressive high-grade pulmonary NETs and showed that both, together and individually, are associated with poor survival.[11] In our study, when we examined the relationship between recurrence and survival, regardless of the typical/atypical carcinoid tumor subtype, we did not find a significant difference between the OTP groups.

In most metastatic diseases that compromise 27% of NETs, the primary tumor cannot be detected despite intensive diagnostic efforts.[18] Clinically, TTF-1 is used to detect primary tumors due to its higher pulmonary specificity. However, Hanley et al.[8] reported the sensitivity in pulmonary carcinoids (66%) and nonpulmonary carcinoids (7%), respectively. The investigators also showed that positive OTP staining in fine-needle aspiration biopsies was specific for pulmonary NETS, and it did not occur in extrapulmonary NETs. In another study on pulmonary NETs, Swarts et al.[14] found OTP positivity in only two cases of small cell lung carcinoma, except for carcinoid tumors. Interestingly, they observed 5 and 10 years of disease-free survival following surgery in these low-grade cases. Nonaka et al.[7] reported only four cases of small cell carcinoma with weak and focal OTP staining. In general, investigators have indicated 66% to 80.9% sensitivity and 80.9% to 100% specificity for OTP and regarded it as superior to TTF-1 in distinguishing pulmonary carcinoid tumors.[8],[12] This study determined the sensitivity of OTP as 66.7%, similar to the literature. We could not determine the specificity of OTP since we only evaluated the pulmonary carcinoid subclass.

Pulmonary carcinoid tumors belong to the NET group and are thought to originate from Kulchitsky cells. NETs range from benign tumors with long life expectancy to tumors with highly aggressive progression.[19],[20] Approaches to treatment and follow-up of this broad range of tumors also differ remarkably according to subtypes. The search for an objective method of tumor typing with immunohistochemical analysis of markers such as Ki-67, CD44, and OTP continues since mitotic count and assessment of tumor necrosis in routine H and E staining can lead to somewhat subjective results.

The main limitation of the study is that only pulmonary carcinoids were evaluated and other organ carcinoids and high-grade NETs of the lung were not included in the study. Therefore, an evaluation could not be made in terms of specificity.

The valuable aspect of our study is that it is one of the first studies in which OTP, one of the immunohistochemical markers that has attracted attention due to its high specificity in pulmonary carcinoid tumors, was used with similar case numbers as in the literature.

In conclusion, OTP is not effective in the subclassification of pulmonary carcinoid tumors. However, the effects of recurrence and survival, which were not detected in our study, need literature support.


Dr. Aydın Yılmaz, chief physician of Atatürk Chest Disease and Thoracic Surgery Training and Research Hospital, contributed significantly to the supply of OTP antibodies. Also Hasan Hüseyin and Serdar, pathology technicians, during a challenging process of working on a new research antibody, made the progress of the work with great dedication.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

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Nonaka D, Papaxoinis G, Mansoor W. Diagnostic utility of orthopedia homeobox (OTP) in pulmonary carcinoid tumors. Am J Surg Pathol 2016;40:738-44.  Back to cited text no. 7
Hanley KZ, Dureau ZJ, Cohen C, Shin DM, Owonikoko TK, Sica GL. Orthopedia homeobox is preferentially expressed in typical carcinoids of the lung. Cancer Cytopathol 2018;126:236-42.  Back to cited text no. 8
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Correspondence Address:
Mehmet Çetin,
MD, Department of Thoracic Surgery, Omer Halisdemir University Training and Research Hospital, Niğde
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijpm.ijpm_210_22


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